In the glass-making art the need occassionally arises to insert electrodes into an operating glass melting tank. A typical case arises when it is desired to add electrical heating to a gas-fired glass melting furnace to either boost the output of the furnace or to reduce the consumption by the furnace of fossil fuels. Or it may be desired to increase the number of electrodes in a furnace already equipped with electric heating. Additionally, when starting up a new furnace designed to include electric heating, it may be desirable to insert the electrodes after operation has begun.
Because inserting an electrode into an operating glass melting furnace entails drilling through the refractory walls or floor of a molten glass tank below the level of the melt, considerable hazard may be involved. Particularly crucial is the timing of the withdrawal of the drill and insertion of the electrode into the bore. Undue delay at this time can result in the molten glass escaping through the bore which, if uncontrolled, can be a hazard to personnel and may substantially disrupt the glass-making operation.
The typical prior art approach to inserting an electrode into a glass melting tank has been to advance a drill on a stand into the refractory until the bore extends almost through to the molten material, leaving a thin, frangible plug at the end of the bore. The drill is then retracted from the bore, the drill stand moved aside, and an electrode brought into alignment with the bore on a hoisting mechanism. When the electrode has been accurately aligned with the bore, the electrode is forced into the bore by hydraulic cylinder means and brought to bear against the plug of refractory material remaining at the end of the bore so as to break out the plug and drive the electrode into the molten material. During the critical time between the withdrawal of the drill and the insertion of the electrode, streams of water are directed into the bore to prevent a breakthrough of the molten glass. Because of the hazards associated with this critical time period, it would be highly desirable to expedite the electrode inserting step, thereby shortening this critical period.